Hydraulic brake booster



Oct. 3, 1944. w. STELZER 2,359,687

HYDRAULIC BRAKE BOOSTER Filed Aug. 29, 1942 4 Sheets-Sheet l N N Na M MN m NM WN MN Sm N w INVENTOR.

Oct. 3, 1944. w sT z 2,359,687

HYDRAULIC BRAKE BOOSTER Oct. 3, 1944. w, STELZER 2,359,687

HYDRAULIC BRAKE BOOSTER INVEN TOR.

Oct. 3, 1944. w. STELZER HYDRAULIC BRAKE BOOSTER 4 Sheets-Sheet 4 Filed .Aug. 29, 1942 xkm liv I Ill/47 Patented Oct. 3,

UNITED STATES PATENT OFFICE HYDRAULIC BRAKE noos'rnn' William Stelzer, Detroit, rm. Application August '29, 1942. Serial No. 456,652

Claims. (01. 60-5415) The invention relates to hydraulic brake boosters and more particularly to a hydraulic brake booster for increasing the hydraulic pressure in a braking system, using a power operated 'expansible chamber motor mechanism controlled by the reaction of the manually produced fluid pressure and the reaction of the boosting force.

The object of the invention is to provide a novel construction to utilize the reaction of the: primary or low pressure cylinder to regulate the flow of power to and from the booster in order to maintain a pre-determined booster ratio.

Another object is to balance the reaction of the primary cylinder against the reaction of the power operated expansible chamber motor mechanism, to utilize the elements required for boosting the. fluid pressure also for the purpose of control whereby the usual fluid pressure sensitive elements used to govern thevalve may be dispensed with and the construction greatly simplified.

The invention also aims to. provide a novel construction that lends itself ideally for mass production', by the obviation of complicated and numerous parts.

Other advantages and features will become apparent by inspection of the drawings, wherein: Fig. 1 is a cross sectional side elevation of the improved hydraulic booster, connected to a conventional hydraulic braking system shown 'diagrammatically;

Fig. 2, a cross sectional side elevation showing I the booster in amodifled construction;

Fig. -3, a front elevation of the balancing plate used in the construction shown in Fig. 2;

Fig. 4, a cross sectional side elevation of the booster showing a further modification;

Fig. 5, a fragmentary cross sectional-side ele' vation of the booster shown in Fig. 1, illustrating the operating position of the valve elements when the pedal is depressedand the booster becomes energized;

Fig. 6, a similar view of the construction shown in Fig. 1, illustrating the fholding position? of the booster where the pistons have advanced to apply the brakes and the power or force of application is held, but not increased;

Fig. '7, a fragmentary cross sectional side elevation of the construction shown in Fig. 2. illustrating the operating position where the booster becomes energized;

Fig. 8. a similar view of the construction shown in Fig. 2, illustrating the holding position;

Fig. 9, a fragmentary cross sectional side elecircuit.

vation of the construction shown in Fig. 4, illustrating'the operating position where the booster becomes energized; and

Fig.. 10, a similar view of the. construction shown in Fig. 4, illustratingthe holding position.

Describing the invention now more in detail, and referring in particular to Fig. 1, there is shown a conventional hydraulic braking system consisting of a master cylinder I operated by the operator anda plurality of wheel cylinders 2, of which only one is shown in order not to encumber the drawings. Fluid pressure line 3 is shown branching oil to lead toother wheel cylinders or fluid pressure receiving'means' in which a boosted pressure is required. Interposed between the master cylinder and the wheel cyl-' inders of. this conventional braking system is I the novel. brake booster, whereby the fluid pres-- the master power reservoir and. to house theexpansible' chamber motormechanism consisting of piston in and power cylinder ll adapted to slide endwise a short distance. The central portion of power piston in forms a part of the hydraulic piston 12 whose ends ar sliding in the hydraulic cylinders 5 and 1 and are provided with seals i3 and II respectively. A fluid passage I 5 accommodating a rod l6 to hold a check valve consisting of a ball I! and spring l8 open when the booster is in the "off" position, serves to provide communication between the primary circuit and when the booster is not in- ,operation.

the secondary circuit While the secondary. cylinder is rigidly. connected to the housing, of the booster, which may be securely mounted to a structural member of the vehicle in which this bralflng' system is'used,

the primary cylinder 5 'is adapted to slide relativeto shell 8 and for this purpose is slidably held by cover 9 and air cleaner cover I! to move in axial, alignment with cylinders I and l I.

The primary cylinder 5 has a collar or piston l2 as well as.

' inder so is shoulder 20 acting against a balancing plate 2| which is shown in detail in Fig. 3 and which may be considered as a plurality of balancing levers whose fulcrum is at 22 where an annular rib is provided in cover 9. Thus plate 2| asillustrated in Fig. 3. is equivalent-to eight separate levers arranged radially. Their central portions are joined together merely to hold the lever in the v proper position. Since the joining strips of metal near the circular line in contact with fulcrum 22 are relatively narrow, the resistance oflered by themagainst flexion is small. The outer extremity of balancing plate 2| is in contact with power cylinder ll so that the reactions of the latter and cylinder oppose each other and operate valve 82 which is slidably fitted on cylinder 5 and controls the passage of air through hole 23 into chamber 24 as well as the evacuation of air from chamber 24 through passage 21 into vacuum chambers 25 and 26 communicating through-the clearance space between shell I and cylinder ll. 51 indicates a source of vacuum'or low pressure such as the intake manifold of an internal combustion engine, connected to vacuum reservoir-"or housing I through a line I8. As a source of pressure to operate piston i0 I utilize th atmosphere in this preferred em- ..trol cylinder 4|,- it is guided by and adaptedto move endwise in air cleaner housing I! and the central portion of the cylinder sides of .power cylinder 31 and control cylinder 4| secured together where a seal 52 is provided to prevent flow of air from pressure chamber 45 into vacuum chamber 40.

Having thus described the details of the novel construction. I shall now illustrate the operation i of the same, referring in particular to Fig. l,

which'shows the booster in the "ofl position.-

where the moving-members are retracted, the

pressure in the master cylinder relieved, and

Y the supply'of power is cut oil! from the expansible bodiment. whereby the air is permitted to enter through holes into chamberjl containing a iiltering material. A slidable seal 32' pressed against cover 9 by a spring "prevents air from passing directly into chamber It is app ent that instead of atmospheric pressure any other,

source of pressure may be without changing the principle of the invention.

Pistons Ill and I2 are urged into the o "position as shown by a-return spring 28, whereby power piston il comes to rest against valve '2. In order to permit free passage of'air between I the'twoparts one or aplurfl ty of radial grooves 2; is provided. Spring 59 serves to urge said valve into a closedposition as well as to p event the use of power when. the brake effort is very small. 7 s

In the embodiment shownin 2 chamber 26 is formed by a fixed power cylinder Oil in which pistons l4 and 4| slide. The latter engages, valve 42 and base. central opening which provides an air passage 2. The outer portion of the control piston 6| engages balance plate 2| whereby the function of piston 4 is similar to that of cylinder ii in Fig, 1. A passage 34 provides communication between vacuum chambers 25 and 2!. while 'the construction illustrated'in Fig. l is particularly suited for use in vehicles where the booster 26, the pressure in chamber 24 'urging cylinder.

ber 24 via passage 21.

chamber motor mechanism. Due to the source oivacuum 51 a low pressure exists in chambers 24; 25, and 26. The vacuum pressure from chamber 24 is communicated to chamber 25 through the'clearance space between cylinder II and housing 8. The evacuation of chamber 24 results from the action of valve 62 which is un.- seated from, cylinder II when the pressure in.

chamber 24 is greater than in chambers 25 and towards the right, which movement is transmitted through plate 2| to cylinder 5 to force the latter towards the left, whereby communication is established between chamber 25 and chamchamber 24 also reacts on piston plate I0 to urge it towards the left, spring 22- is of suflicient i strength to resist the movement of piston ill and to cause spring 59 to yield first, i. e., the air pressure in chamber 24 acting on cylinder urges ,the latter towards the right against lever member 2| which transmits the movement to cylinder I to force it to the left. together'withvalve 62 and piston HI, so that thevalve becomes unseated and the air can escape from chamber 24 into Hand 26 until the pressures are equalized. Assuming; now that the operator depresses the brake pedal to apply thesbrakes, hydraulic. fluid is transmitted from the master cylinder I through line 4' into chamber 54, passage l5, chamber 55, and line 2 to the wheel cylinders2 whose is exposed-to the impact-of. stones or other obiects. because the outer 0 55 1 8. servesas a protective armor where dents orxblowsdonotaii'ect the operation of'the booster, the modification shown in Fig; zinay jbe where .the' booster abuse. 1

Fig. 4 shows'a further modification where the balancingplate is eliminated. and control piston 25 and primary cylinder "are of .one piece to of suiiicient rigidity to withstand pistons expand to' apply the brake shoes. As soon .as the brake shoes come intocontact with the brake drum the resistance'to further expansion increases and consequently the operator "has to exert a greater manual efl'ortresultmg in I is mounted ina protected position or where cyl-- an in'creased hydraulic, pressure in the-entire system, with an accompanying increase in reactionacting on primary cylinder 5. This re- 7 action is transmitted by shoulder to plate 2| which reverses the force to act in the opposite directionagainst cylinder H which again transmits the force to piston I 0 through the intermove in unison. Power piston It moves incylinder 21- closed by a cover 20 secured to secondary cylinder 1 to form a vacuum chamber 39; The

latter is in communication with chamber 440i control cylinder 4| by means of passage 42. 43'

denotes an end plate secured to cylinder 4| to form a chamber 44 communicating permanently T with chamber 45 of the power cylinder through mediary of'vaive 62', tending to overcome spring 2.. The stillness of spring 28 determines the point where the'boosterbecomes operative. To

conserve thesupply of power it is desirable that the-booster doesnot go into action until the force exerted by the operator becomes noticeable. As

the reaction of cylinder I overpowers spring 28 piston'ilas well-as valve 82 and cylinder Ilmove away from cylinder 5 so that a passage is While the pressure in opened at 56 to admit air from the atmosphere through air cleaner l9 and port 23 into chamber 24, passing through grooves 29. The'position of the elements at this stage of the operation resultant pressure in the secondary circuit is the sum of the primary pressure acting on piston l2 and the air pressure acting on power piston HI. Consequently, the proportion between the power cylinder II and primary cylinder 5 determines the booster ratio. :However, the latter also depends on, the leverage of balancing plate 2|.

Thusfif fulcrum point 22 is moved farther out, the predetermined booster ratio is greater. The boosting force is constantly in a pre-determined proportion to the primary pressure which. is the result of the pedal pressure exerted by the operator. Assuming that too much air pressure exists in chamber 24, which may occur when the operator reduces the manual pressure on the brake pedal, cylinder ll, immediately overpowers cyl-.

inder 5 whereby cylinder H advances towards plate 9 and the primary cylinder retracts in the opposite direction, carrying valve 22 with it to close passage 56 and opening a passage from chamber 24 through 21 into chamber 25 against the pressure of spring 59, allowing chamber 24 to relieve its pressure until the power booster and the primary when valve 62 assumes a holding position where passages 21 and 55 are closed oiiias shown in Fig. 6. To prevent valve 52 to open or close due to the slightest pressure differences, it is desirable that spring '59 urges valve 62 into a closed position with a sumcient force. Assuming now that the operator releases his pressure on thebrake pedal and consequentiyrelieves the pressurein the primary circuit, cylinder ll immediately moves towards plate 9 until it comes to rest against it with the outer extremity of balpressure are balanced again as valve I1 is closed. The position of the elements when air is admitted to chamber 44 is illustrated in Fig. 9. The reaction of the primaryvpressure oncylinder 36 is counteracted and balanced by the fluid pressureof the power fluid admitted to the booster by acting on the control piston 35, the size of which determines the booster ratio. When too much power fluid is admitted to the booster, piston 35 overpowers cylinders 36, allows valve 48 to seat on plate 43 and thenunseats shoulder 50 from valve 49 to allow relief of air pressure from chamber 45 through passages 41, 48, and 52 into low pressure chamber and 39. The holding position, where the brakes are held applied and the pressure'in chamber is in the proper proportion to the manually produced pressure in chamber 54, is illustrated in Fig. 10. When the operator releases the brake pedal entirely with a consequent reduction of the force of reaction of cylinder 36, the existing air pressure in chamber 44 immediately actuates piston 35 to unseat shoulder 50 to allow the air in chambers 44 and 45 to evacuate through passage 52 and 42 until a vacuum exists in chambers 44 and 45. At

the same time spring 28 returns piston 12 to the off position as shown, unseating ball H to allow fluid to flow from thewheel cylinders to the master cylinder. It will be. noted that in the ofi position of the booster chamber 45 is in communication with the :lo'w pressure through passages 41, 48, and 52. The communication is established due to the existing pressure in cham her which urges piston 35 to the left willciently .to unseat shoulder 50. After the pressure in chambers 44 and 45 is relieved piston 35 may move to the right again due to the residual hydraulic pressure in the brake line, acting in chamber 54, which, however, is not sui'licient to ancing plate 2| interposed, forcing cylinder 5 in Y the opposite direction and opening valve 62 to relieve the pressure from chamber 24 into chamber 25 and 26. The remaining pressure in cylinder 1 combined with spring 28 urges piston l2 into the ofP' position as shown in Fig. 1, causing ball I] ,to unseat to establish communication between the primary and secondary circuits.

The operation of the modified booster shown in I Fig. 2 is very similar The function of piston 6| as f r as the operation to that described for Fig. 1.

a direction to increase the volume of chamber 54 whereby valve 49 is p'icked'up and unseated from plate 43 to allow air to pass through passage 46 into chamber 44 as well as into chamber 45 through passage 41, urging piston ill to advance to force piston l2 to enter secondary cylinder 1 to boost the secon'dary pressure as soon compress spring 5| after shoulder 50 hascome in contact with valve 49.} I

In order to operate the control valve only a very small movementof the primary cylinder is required. This isparticularly true of.the embodiment shown in Fig. 1 where the valve travel is augmented due to the relative movement of cylinder 5 and power cylinder H. height of the welt or annular rib 22 maybe much smaller than shown, having been exaggerated in the drawings in order to make a clear illustration.

While I'have shown sliding type pistons in a diagrammatic manner, it is apparent that any other type of piston may be used, particularly the diaphragm type, without departing from the principle of theinvention.

, Having shown three different embodiments by way of example, I do not wish to be limited to these particular embodiments except by the terms of the appended claims.

I claim:

1. In a hydraulic system having hydraulic pressure producing means and hydraulic pressure receiving means, in combination, a booster un t comprising a primary cylinder in communication with said hydraulic pressure producing means a secondary cylinder in communication .wth said hydraulic pressure receiving means; a piston in said secondary cylinder to force hydraulic fluid tosaid hydraulic pressure receiving means, a piston in said primary cylinder to transmit the force of the liquid in said primary cyl nder to act on said piston in said secondary cylinder, an expansible chamber motor mechar' nism to act on said piston in said secondary cyl- Thus the inder to boost the hydraulic pressure in the latter, said primary cylinder being arranged to slide endwise a short distance, power fluid to operate said 'expansible'chamber motor mechanism, valvemeans to direct power fluid to and from expansible chamber motor mechanism, means to transmit the reaction or the pressure of the power fluid directed to said expansible chamber motor mechanism to act omsaid primary dralllic flllid'in the latter to said piston in said secondary cylinder tol. increase the hydraulic pressure'in said secondary cylinder, an expansible chamber motor mechanism to exert a force on the piston in said secondary cylinder to boost i the pressure therein, said primary cylinder being mounted to' yield a short distance to the prestherein,"power fluid to operate said expansible chamber motor mechanism, and. valve means responsive f to the yield of said primary cylinder to direct power fluid to and from said expansible chamber motor mechanism.

3. The construction as claimed in claim 2, and

means where the yield of said primary cylinder is opposed by the reaction of said expansible chambermotor mechanism.

4. Th construction as claimed in claim 2, and

means responsive to the pressure'oi. the power fluid directedto said expansible chamber motor rm'ichanisn'i to oppose the yield of said primary cylinder.

5. The construction asclaimed in 2 where saldexpansible chamber motor mechanism is mounted-yieldinsly, means to transmit the reaction of said-expansible chamber motor mechanism tooppose the yield of said primary cylinder,

6. In a hydraulic braking system having a master cylinder operated by the operator and wheel cylinders "to operate the brake shoes, in

combinatioma primary cylinder, fluid pressure transmitting means ircmsaidprimary cylinder to-said: cylinder, a secondary cylinder, fluid pressure transmitting means from said secondary cylinder to saidlwheel' cylinders, an expansibie chamber'motor mechanism to boost the pressure-in said secondary cylinder, 9'. supply "oipower fluid to operate said expansible chamber motor mechanism, aplston in said primary'cylin der to actuate a piston in said'secondary cylin- 'a secondary cylinder connected to a secondary circuit, a piston in said secondary cylinder, a piston in said primary cylinder to superimpose the pressure oi! said primary circuit on the pressure of said secondary circuit, an expansible chamber motor mechanism to act on said piston in said secondarycylinder to increase the hydraulic pressure therein, a supply of power to operate said expansible chamber motor mecha-,

nism, said primary cylinder being able to move endwise a short distance in order to be responslve to the reaction due to the internal pressure in said primary cylinder, means responsive to the power exerted by said expansible chamber motor mechanism to oppose the movement oi said primary cylinder, and valve means cooperating with said prlmarycylinder to maintain the power exerted by said expansible chamber motor mechanism in proportion with the hydraulic ressure in said primary cylinder.

-8. In a hydraulicj braking system having a master. cylinder operated by the operator and wheel cylinders to apply the brakes, ahydraulic booster comprising a primary cylinder in communication'with said master cylinder, a secondary cylinder in-communication with said wheel cylinders, apiston in said secondary cylinder to.

force hydraulic fluid to said wheel, cylinders, a piston in said primary cylinder to transmit the force of hydraulic fluid in the latter to said histon insaid secondary cylinder to increase the hydraulic pressure in said secondary cylinder, an expansible chamber motor mechanism to exert a force on the piston in said secondary. cylinder to boost the pressure therein, said primary cylinder 1 and said expansible chamber motor mechanism Y beingmounted to be able to yield a short distance 4 due to" their reactions, power fluid to operate said expansible chamber motor mechanism, said valve lic pressurein said primary cylinderto the fluid insaid secondary cylinder, an expansible' cham- 'ber. motor mechanism consisting'oi a power cyl- -linder'=havlng a. power piston, said power piston der to transmit thehydraulic pressure from said primary cylinder to said secondary cylinder, said primary cylinder being mounted to be able to move endwise, means to transmit the force or reaction acting on said primary cylinder to oppose the reaction oisaid supply or power fluid acting on said expansible chamber motor mechanism, and valve means responsive to the excursions of said primary cylinder to direct power fluid a and from said expansible chambermotor mechanism '1. A hydraulic seam booster having-impriexpansible chamber motor mechanism, valve means to direct power fluid to and from said means being responsive to ,the movements oisaid primary cylinder and said expansible chamber motor mechanism whereby the yield 0: said primary cylinder, urges said valve. meansto direct power fluid to said'expansible chamber motor andithe yield oi. the latter urges said valve means to direct power fluid from said expansible chamber motor mechanism.

- mary cylinder connected to a primary circuit, a secondary cylinder connected to a'secondary cir-v 1- .cuit, a piston in said secondary cylinder, a pis-' 9; A hydraulic pressure booster having a priton in said primary cylinder, said pistonsbeing mechanically connected to transmit the hydraubeing arranged to assist safid'pist'on in said secondary cylinder to boost thehydraulic pressure therein, said power cylinder being arranged to I allow alimited motion endwise, said primary cylinder being also arranged-to permit a limited motion endwise, means to counterbalance said power cylinder against said primary cylinder so that the reaction or said power cylinder opposes the reaction oi-said primary cylinder, valve means responsive to the excursions of said primary cylinder and said power cylinder due' to their unbalancement to direct power fluid to and from said expansible chamber motor mechanism mary cylinder connected to a primary circuit,

whereby the reaction of said primary cylinder urges saidvalve to increase the power of said expanslble chamber motor mechanism and the reaction of said power cylinder urges said valve to decrease the power of said expansible chamber motor mechanism.

10. Theconstruction as claimed 'in claim 9 where said expansible chamber motor mechanism is enclosed in a housing which serves as a vacuum reservoir and as a protective enclosure for said expansible motor mechanism,

11. The construction as claimed in claim 9, and means to provide a fluid passage between said primary cylinder and said secondary cylinder when said hydraulic pressure booster is in the off position,

12. The construction as claimed in claim 9, and means to return said pistons to the ofi position. v

a 13. The construction as claimed in claim 9,

where said primary cylinder, said secondary cylinder, said expansible chamber motor mechanism,

said pistons, said means for counter-balancing,

and said valve means form a single, self-contained unit.

14. A hydraulic pressure booster having a primary cylinder connected to a primary circuit, a secondary cylinder connected to a secondary circuit, a'piston in said secondary cylinder, a piston in said primary cylinder connected mechanically to said piston in said secondary cylinder to transmit the hydraulic pressure in said primary cylinder to said secondary cylinder, an expansible chamber motor mechanism having a power cyllatter being connected to assist said piston in said secondary cylinder to boost the hydraulic pressure in said secondary circuit, a supply of power fluid, a control piston slidable a short distance in said power cylinder and responsive to the power acting on said power piston, said primary cylinder being arranged to be able to move endwise a short distance in order to be responsive to the reaction due to the hydraulic pressure in said primary cylinder, means to transmit the pressure acting on saidvcontrol piston to oppose the reaction of said primary cylinder, valve means operated by the excursions of said primary cylinder to direct power fluid to and from'said expansible chamber motor mechanism, whereby the reaction of said primary cylinder urges said valve to increase the power of said expansible chamber motor mechanism, and said control piston STELZER. 

